perf: arm_cspmu: Fix variable dereference warning

perf: arm_cspmu: Fix variable dereference warning

Fix warning message from smatch tool:
  | smatch warnings:
  | drivers/perf/arm_cspmu/arm_cspmu.c:1075 arm_cspmu_find_cpu_container()
  |    warn: variable dereferenced before check 'cpu_dev' (see line 1073)

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Link: https://lore.kernel.org/r/202302191227.kc0V8fM7-lkp@intel.com/
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Besar Wicaksono <bwicaksono@nvidia.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20230302205701.35323-1-bwicaksono@nvidia.com
Signed-off-by: Will Deacon <will@kernel.org>